1. Field of the Invention
The present invention relates to an image forming apparatus wherein an image on a document is converted to an electrostatic latent image by an electrostatic image forming process, and toner is supplied to the latent image, thereby a toner image is formed to be printed out on a sheet material.
2. Description of the Related Art
An image forming apparatus, e.g., a copying apparatus has an image reading section for reading an image of a document, an image forming section for forming a toner image from the image read by the image reading section, and a material conveying section for conveying sheet materials for holding the toner image formed by the image forming section.
The image reading section has a document table on which the document is mounted, and reads the image of the document as image data, and transmits image data to the image forming section.
The material conveying section includes a plurality of cassettes, which can contain a plurality of types of paper having a different size and a different direction, and a multi-stage paper feeding device (expansion feeding device), which can feed paper having a different size and a different direction, and at least one of conveyor devices conveys the paper having a desired sized to the image forming section.
The image forming section has a photoconductive drum, a developing device, and a copy starting switch. On the photoconductive drum, an electrostatic latent image is formed in accordance with image data. The developing device supplies toner to the latent image formed on the photoconductive drum to be developed. The copy starting switch designates the start of copying to start the image formation. Then, the image forming section outputs the image formed based on image data to paper conveyed by the conveying section.
Paper materials are contained in each cassette, and picked up one by one from the top in order. The picked up one paper is conveyed to the photoconductive drum of the image forming section by a plurality of conveying rollers arranged in the apparatus. Then, the top edge portion of paper is arrived at an aligning roller arranged in the vicinity Of the photoconductive drum, and once stopped in a state that paper itself is curved.
The top edge portion of paper collides with the aligning roller, so that an inclination of the top edge in the conveying direction, which occurs when paper is conveyed from the cassette by the conveying rollers, is removed. After paper is temporarily stopped by the aligning roller, paper is conveyed to the photosensitive drum of the image forming section in a state that timing between the top edge of the image formed on the photoconductive drum and the top end of paper is matched when the aligning roller is rotated. Then, the paper is conveyed to the photoconductive drum of the image forming section, and receives the image formed on the photoconductive drum.
A detector, which detects a back edge of paper being conveyed to the aligning roller, is provided at a predetermined position of the side of conveying rollers. At the time when the back edge of paper is detected by the detector, next paper is picked up from the same cassette.
In this way, next paper is picked up in advance after paper conveyed to the photoconductive drum, thereby time necessary for continuous copying can be reduced.
In the above apparatus, a distance between the desired cassette and the photoconductive drum, i.e., a paper conveying distance is increased as the apparatus is large-sized and a plurality of cassettes is provided. The paper conveying distance is further increased as the apparatus has the multi-stage paper feeding device. In other words, as the paper conveying distance is longer, there is needed increase in the number of mechanisms for removing an inclination of a top edge and the number of detectors.
However, in the case that the plurality of the inclination removing mechanisms and the detectors are provided, when the first paper is stopped by the inclination removing mechanism, which is the closest to the photoconductive drum, there occurs a case that a next picked up paper is stopped between the inclination removing mechanism and the detector, which are provided in the middle of the paper conveying, due to the length of the paper and slight change of the conveying speed. In this case, there often occur the problems that the next picked up paper and a sequentially picked up paper 10 are collided with other and that the papers are jammed. Also, the next picked up paper and the sequentially picked up paper may be jammed at the portion close to the photoconductive drum or wound around the photoconductive drum.